1. Field of the Invention
The present invention relates to a piezoelectric power generation device that can obtain output current substantially two times as much as that of a piezoelectric power generation device using a usual piezoelectric ceramics element and can prevent the parasitic resonance of a metal electrode.
2. Description of the Related Art
A piezoelectric material has various application aspects as a converting element between mechanical energy and electrical energy. As materials showing a piezoelectric effect, many materials of both inorganic materials and organic materials are well-known. As materials that are currently put to practical use, materials such as a PZT type ceramics (piezoelectric ceramics) are exemplified.
The piezoelectric ceramics element is an element provided with piezoelectric characteristics formed in such a way that high DC voltage is applied to a polycrystalline material to generate remanence. Because a basic piezoelectric constant can be relatively freely changed depending on the composition of the piezoelectric ceramics element, a use thereof is wide. Especially, the piezoelectric ceramics element composed of lead zirconate titanate (PZT) has a wide selection range of composition ratio or additives and a variety of application ranges.
FIG. 7 is an explanatory view of a usual piezoelectric power generation device. The piezoelectric power generation device is formed by uniting a piezoelectric ceramics element plate 31 to a base 32 made of an acrylic material and fixing both the end parts of the base 32 by holders 33 made of a hard material such as metal. Then, a steel ball 35 is dropped on the ceramics element plate 31 to apply mechanical impact energy due to a collision to the piezoelectric element plate 31, excite a flexural oscillation on the piezoelectric element plate 31 including the base 32 and take out electric energy.
However, although the practicability of the usual PZT type piezoelectric ceramics element is anticipated, a quantity of generated energy is very small. Thus, the usual PZT type piezoelectric ceramics element is undesirably deficient in its practicability for the piezoelectric power generation device. In the power generation device using the piezoelectric ceramics element of this type, the natural oscillation of the piezoelectric ceramics element plate 31 essentially needs to be continued as long as possible. Therefore, a support structure needs to be realized that the natural oscillation of the piezoelectric ceramics element plate 31 does not accompany a mechanical resistance. Further, in the above-described related art, because the material of the base 32 is different from the material of the piezoelectric ceramics element plate 31, a center of oscillation (a part that does not expand and contract) is hardly disposed on a uniting surface of the base 32 and the piezoelectric ceramics element plate 31. When the center appears in the piezoelectric ceramics element plate 31, a cancellation in a polarization is undesirably generated to lower power generation efficiency.
In order to solve the above-described problems of the usual power generation device, the applicant of the present invention previously proposes a piezoelectric power generation device (disclosed in Japanese Patent Application Laid-Open No. 2001-145375) shown in FIG. 8. In this piezoelectric power generation device, two plate shaped piezoelectric ceramics elements 1a and 1b are united to each other with polarization set to opposite directions to form laminar piezoelectric ceramics members 1 (PZT1) and 1 (PZT2). Then, one surface of each of the piezoelectric ceramics members 1 and 1 is struck to generate power. Thus, the power generation device good in its power generation efficiency and effective in small power generation is obtained.
It is a first object of the present invention to provide a piezoelectric power generation device excellent in its power generation efficiency in which polarization is set to the same direction differently from the previous application and an extremely thin metal electrode is sandwiched between piezoelectric ceramics elements so that a current output obtained in the piezoelectric power generation device with the above-described structure previously filed by the applicant of the present invention can be improved substantially to about twice as high as the previous current output.
It is a second object of the present invention to provide a piezoelectric power generation device that can greatly improve power generation efficiency by forming different level parts in a piezoelectric ceramics member and a metal electrode to eliminate a parasitic resonance in the piezoelectric power generation device.